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Using an Expressive Description Logic: FaCT or Fiction?
 In Proc. of KR98
, 1998
"... Description Logics form a family of formalisms closely related to semantic networks but with the distinguishing characteristic that the semantics of the concept description language is formally defined, so that the subsumption relationship between two concept descriptions can be computed by a suitab ..."
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Cited by 273 (53 self)
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Description Logics form a family of formalisms closely related to semantic networks but with the distinguishing characteristic that the semantics of the concept description language is formally defined, so that the subsumption relationship between two concept descriptions can be computed by a suitable algorithm. Description Logics have proved useful in a range of applications but their wider acceptance has been hindered by their limited expressiveness and the intractability of their subsumption algorithms. This paper addresses both these issues by describing a sound and complete tableaux subsumption testing algorithm for a relatively expressive Description Logic which, in spite of the logic's worst case complexity, has been shown to perform well in realistic applications. 1 INTRODUCTION Description Logics (DLs) form a family of formalisms which have grown out of knowledge representation techniques using frames and semantic networks
Tableau Algorithms for Description Logics
 STUDIA LOGICA
, 2000
"... Description logics are a family of knowledge representation formalisms that are descended from semantic networks and frames via the system Klone. During the last decade, it has been shown that the important reasoning problems (like subsumption and satisfiability) in a great variety of descriptio ..."
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Cited by 265 (27 self)
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Description logics are a family of knowledge representation formalisms that are descended from semantic networks and frames via the system Klone. During the last decade, it has been shown that the important reasoning problems (like subsumption and satisfiability) in a great variety of description logics can be decided using tableaulike algorithms. This is not very surprising since description logics have turned out to be closely related to propositional modal logics and logics of programs (such as propositional dynamic logic), for which tableau procedures have been quite successful. Nevertheless, due to different underlying intuitions and applications, most description logics differ significantly from runofthemill modal and program logics. Consequently, the research on tableau algorithms in description logics led to new techniques and results, which are, however, also of interest for modal logicians. In this article, we will focus on three features that play an important role in description logics (number restrictions, terminological axioms, and role constructors), and show how they can be taken into account by tableau algorithms.
Practical reasoning for very expressive description logics
 Journal of the Interest Group in Pure and Applied Logics 8
, 2000
"... Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm t ..."
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Cited by 188 (23 self)
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Description Logics (DLs) are a family of knowledge representation formalisms mainly characterised by constructors to build complex concepts and roles from atomic ones. Expressive role constructors are important in many applications, but can be computationally problematical. We present an algorithm that decides satisfiability of the DL ALC extended with transitive and inverse roles and functional restrictions with respect to general concept inclusion axioms and role hierarchies; early experiments indicate that this algorithm is wellsuited for implementation. Additionally, we show that ALC extended with just transitive and inverse roles is still in PSpace. We investigate the limits of decidability for this family of DLs, showing that relaxing the constraints placed on the kinds of roles used in number restrictions leads to the undecidability of all inference problems. Finally, we describe a number of optimisation techniques that are crucial in obtaining implementations of the decision procedures, which, despite the hight worstcase complexity of the problem, exhibit good performance with reallife problems. 1
Reasoning with Individuals for the Description Logic SHIQ
, 2000
"... While there has been a great deal of work on the development of reasoning algorithms for expressive description logics, in most cases only Tbox reasoning is considered. In this paper we present an algorithm for combined Tbox and Abox reasoning in the SHIQ description logic. This algorithm is of part ..."
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Cited by 155 (36 self)
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While there has been a great deal of work on the development of reasoning algorithms for expressive description logics, in most cases only Tbox reasoning is considered. In this paper we present an algorithm for combined Tbox and Abox reasoning in the SHIQ description logic. This algorithm is of particular interest as it can be used to decide the problem of (database) conjunctive query containment w.r.t. a schema. Moreover, the realisation of an efficient implementation should be relatively straightforward as it can be based on an existing highly optimised implementation of the Tbox algorithm in the FaCT system.
The FaCT system
 In Proceedings of the International Conference on Automated Reasoning with Analytic Tableaux and Related Methods (TABLEAUX’98), volume 1397 in Lecture Notes in Artificial Intelligence
, 1998
"... Abstract. FaCT is a Description Logic classifier which has been implemented as a testbed for a highly optimised tableaux satisfiability (subsumption) testing algorithm. The correspondence between modal and description logics also allows FaCT to be used as a theorem prover for the propositional moda ..."
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Cited by 151 (15 self)
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Abstract. FaCT is a Description Logic classifier which has been implemented as a testbed for a highly optimised tableaux satisfiability (subsumption) testing algorithm. The correspondence between modal and description logics also allows FaCT to be used as a theorem prover for the propositional modal logics K, KT, K4 and S4. Empirical tests have demonstrated the effectiveness of the optimised implementation and, in particular, of the dependency directed backtracking optimisation. 1
A description logic with transitive and inverse roles and role hierarchies
, 1998
"... transitive roles play an important rôle in the adequate representation of aggregated objects: they allow these objects to be described by referring to their parts without specifying a level of decomposition. In [Horrocks & Gough, 1997], the Description Logic (DL) ALCH R + is presented, which ext ..."
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Cited by 136 (28 self)
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transitive roles play an important rôle in the adequate representation of aggregated objects: they allow these objects to be described by referring to their parts without specifying a level of decomposition. In [Horrocks & Gough, 1997], the Description Logic (DL) ALCH R + is presented, which extends ALC with transitive roles and a role hierarchy. It is argued in [Sattler, 1998] that ALCH R + is wellsuited to the representation of aggregated objects in applications that require various partwhole relations to be distinguished, some of which are transitive. For example, a medical knowledge base could contain the following entries defining two different parts of the brain, namely the gyrus and the cerebellum. In contrast to a gyrus, a cerebellum is an integral organ and, furthermore, a functional component of the brain. Hence the role is component (which is a nontransitive subrole of is part) is used to describe the relation between the brain and the cerebellum: is component ⊑ is part gyrus:= (∀consists.brain mass) ⊓ (∃is part.brain) cerebellum:= organ ⊓ (∃is component.brain) However, ALCH R + does not allow the simultaneous description of parts by means of the whole to which they belong and of wholes by means of their constituent parts: one or other is possible, but not both. To overcome this limitation, we present the DL ALCHI R + which extends ALCH R + with inverse (converse) roles, allowing, for example, the use of has part as well as is part. 1 Using ALCHIR +, we can define a tumorous brain as: tumorous brain:= brain ⊓ (tumorous ⊔ (∃has part.tumorous)) Part of this work was carried out while being a guest at IRST,
Reasoning with Concrete Domains
, 1999
"... Description logics are formalisms for the representation of and reasoning about conceptual knowledge on an abstract level. Concrete domains allow the integration of description logic reasoning with reasoning about concrete objects such as numbers, time intervals, or spatial regions. The importa ..."
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Cited by 64 (11 self)
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Description logics are formalisms for the representation of and reasoning about conceptual knowledge on an abstract level. Concrete domains allow the integration of description logic reasoning with reasoning about concrete objects such as numbers, time intervals, or spatial regions. The importance of this combined approach, especially for building realworld applications, is widely accepted. However, the complexity of reasoning with concrete domains has never been formally analyzed and efficient algorithms have not been developed. This paper closes the gap by providing a tight bound for the complexity of reasoning with concrete domains and presenting optimal algorithms. 1 Introduction Description logics are knowledge representation and reasoning formalisms dealing with conceptual knowledge on an abstract logical level. However, for a variety of applications, it is essential to integrate the abstract knowledge with knowledge of a more concrete nature. Examples of such "co...
Expressive ABox Reasoning with Number Restrictions, Role Hierarchies, and Transitively Closed Roles
, 1999
"... We present a new tableaux calculus deciding the ABox consistency problem for the expressive description logic ALCNH R + . Prominent language features of ALCNHR + are number restrictions, role hierarchies, transitively closed roles, and generalized concept inclusions. The ABox description logic ..."
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Cited by 62 (25 self)
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We present a new tableaux calculus deciding the ABox consistency problem for the expressive description logic ALCNH R + . Prominent language features of ALCNHR + are number restrictions, role hierarchies, transitively closed roles, and generalized concept inclusions. The ABox description logic system RACE is based on the calculus for ALCNH R + . 1 Introduction Experiences with concept languages indicate that at least description logics (DLs) with negation and disjunction are required to solve practical modeling problems without resorting to ad hoc extensions. The requirements derived from practical applications of DLs ask for even more expressive languages. For instance, in [14] the need for transitive roles is demonstrated for representing partwhole relations, family relations or partial orders in general. It is argued that the tradeo# between expressivity and complexity favors the integration of transitively closed roles instead of a transitive closure operator for roles. ...
Experience building a large, reusable medical ontology using a description logic with transitivity and concept inclusions
 In Proc. of the Workshop on Ontological Engineering
, 1997
"... The European GALEN project is developing terminology services based on a large, reusable medical ontology. The ontology is being built using GRAIL, a description logic with transitivity and general concept inclusions. ..."
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Cited by 60 (10 self)
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The European GALEN project is developing terminology services based on a large, reusable medical ontology. The ontology is being built using GRAIL, a description logic with transitivity and general concept inclusions.
Optimising Description Logic Subsumption
 Journal of Logic and Computation
, 1999
"... Effective optimisation techniques can make a dramatic difference in the performance of knowledge representation systems based on expressive description logics. With currentlyavailable desktop computers, systems that incorporate these techniques can effectively reason in description logics with intr ..."
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Cited by 57 (17 self)
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Effective optimisation techniques can make a dramatic difference in the performance of knowledge representation systems based on expressive description logics. With currentlyavailable desktop computers, systems that incorporate these techniques can effectively reason in description logics with intractable inference. Because of the correspondence between description logics and propositional modal logic, difficult problems in propositional modal logic can be effectively solved using the same techniques.